Morphology of the Leaves of Palms. 



25<J 



under the ventral surface of the petiole, and to a much slighter extent, under 

 the dorsal surface ; on the ventral side the penthouse thus produced happens 

 to be a striking object to the eye, and it may possibly become still more 

 noticeable by suffering some further elongation after the invagination of the 

 limb is completed, but these are not reasons which can entitle it to rank as a 

 morphological entity. The conclusion I have reached is that the " ligule " and 

 " dorsal scale " belong to the petiole, and are merely the outcome of the 

 peculiar mode of limb-development characteristic of the Fan-palms. The 

 appearance of these structures in the Fan-palms, and their absence in the 

 Feather-palms, is due to the fact that in the Fan-palms the whole series of 

 invaginations start from the same level, whereas, in the Feather-palms, where 

 the plications occur to right and left of the median rachis, there is no crowding 

 together of the invaginations at a single point. 



My view of the morphology of the " ligule " and " dorsal scale " leads me 

 to suggest that these terms should be dropped, since the structures in 

 question have nothing to do either with ligules or with scale-leaves ; the 

 term ligule will then be left for the tubular ochrea of Desmoncus, etc., to 

 which it rightfully belongs. The best substitutes seem to be " ventral crest " 

 and " dorsal crest," expressions based upon the word " Crista," already used 

 by Drude* for the " ligule." If my interpretation of these structures be 

 accepted, it leads inevitably to the conclusion that the leaf-stalk, both of the 

 Fan- and Feather-palms, is the basal part of a true petiole. 



And now, finally, we have to consider the nature of the leaf-limb. 

 Strikingly different in aspect as are the mature blades of typical Fan- and 

 Feather-palms, there is not, morphologically, any impassable gulf between the 

 two types. If the median rachis is short or non-existent, we get the " fan " 

 form, while, if there be long-continued growth, the " feather " leaf is produced ; 

 the leaves of such a genus as Licualaf show transitional characters. It seems 

 possible that the " fan " type is the older, since the palmate form predominates 

 among fossil Palms, while the Feather-palms are in the majority at the 

 present day.} But the relative age of the two types must at present be 

 treated as an open question, since they were both apparently in existence in 

 the Upper Cretaceous. The evolution of the " feather " from the " fan " (or 

 vice versd) must have occurred more than once in the history of the family, 

 since both types may be found among Palms which are regarded by system- 

 atists as allied. The sub-family Coryphoidea?, for instance, includes two 

 tribes — the Phcenicese, which are feather-leaved, and the Sabalete, which are 



* Drude, O. (1889). 



t Wendland, H. (1879). 



} Unger, in Martius, K. F. P. von (1823-50). 



